1. Field of Invention
The invention is related to an actuator, comprising a housing, a nut and a screw one of which is axially fixed with respect to the housing and the other of which is axially displaceable with respect to the housing for moving an actuating head, as well as an electric motor which comprises a stator connected to the housing, and a rotor which is drivingly connected to a rotatable part of the screw actuator, the housing having a bore accommodating at least the nut and/or screw, an axially fixed part of said nut or screw being supported with respect to a radial support abutment which extends inwardly in the bore.
2. Description of Related Art
Such actuator is known. The axially fixed part of the screw or nut is firmly pressed onto the radial support abutment as the actuating head is pressed outwardly against a member which is to be actuated. In this way, a simple and reliable support of the screw and nut in the housing is obtained.
The object of the invention is to further simplify the screw actuator construction, while maintaining the relatively simple and sturdy layout thereof. This object is achieved in that the rotor of the motor is supported rotatably on a sleeve, said sleeve engaging the fixed part and extending away from the actuator head, said sleeve having a radially outwardly extending sleeve flange which is interposed between said support abutment, and the axially fixed part.
In particular, the flange of the sleeve is supported on an abutment surface of the support abutment, which faces the actuating head connected to the axially displaceable nut or screw for exerting a compressive force.
The rotor sleeve is now held firmly clamped between the radial support abutment and the axially fixed part of the nut or screw, which provides a simple, reliable construction. No additional fastening means are necessary for supporting the rotor sleeve.
In a practical embodiment, the nut is fixedly supported within the housing, said nut having a radially outwardly extending nut flange facing the outwardly extending sleeve flange and overlapping the inwardly extending actuator support abutment.
In service of the screw actuator according to the invention, misalignment may occur as a result of eccentric forces and/or transverse forces. Such misalignment might cause damage to the balls and raceways of the nut and the screw, which are rather vulnerable to such loadings. According to the invention, this problem can be alleviated in case the outwardly facing surfaces of sleeve flange and the nut flange are curved in axial cross section, so as to allow swivelling or tilting of said nut and sleeve due to misalignment forces.
The screw/nut unit, as well as the drive unit including rotor and possible reduction means, may now move in unison so as to adapt to the misalignment.
A very stable embodiment is obtained in case the nut has a nut extension extending beyond the nut flange and inside the support abutment, the sleeve having an axially extending support part which is accommodated between said nut extension and the support abutment.
According to a preferred embodiment, the actuating head engages the screw through a rolling element bearing. Said rolling element bearing is integrated with the actuating head. A further improvement concerning stability is obtained in case the actuating head is accommodated in a cylinder, which is held non-rotatably in the bore.
The sleeve may comprise a sheet metal part which is provided with the inner raceway of at least one support bearing for rotatably supporting the rotor; alternatively, a separate bearing may be mounted with its inner ring on said sleeve.
For ease of handling and assembly, the sleeve and the nut are clampingly pre-assembled.
The sleeve may furthermore comprise an inwardly extending flange at its end opposite the sleeve flange, which flange carries a gear wheel of the gear reduction mechanism.
The invention is also related to a brake calliper for a disc brake, comprising a claw piece which carries at least two brake pads which enclose a gap for accommodating a brake disc, an actuator comprising a nut and a screw one of which is axially fixed with respect to the claw piece and the other of which is axially displaceable with respect to the claw piece for moving the brake pads towards and from each other, as well as an electric motor which comprises a stator connected to the claw piece, and a rotor which is drivingly connected to a rotatable part of the screw actuator, the claw piece having a bore accommodating at least a part of the screw actuator, an axially fixed part of the screw actuator being supported with respect to a radial support abutment which extends inwardly in the bore.
According to the invention, the rotor of the motor is supported rotatably on a sleeve, said sleeve engaging the fixed part of the screw actuator and extending away from the brake pads said sleeve having a radially outwardly extending sleeve flange which is interposed between said support abutment, and the axially fixed part of the screw actuator.